Fix 500 error in BlobController#delete

If a validation or other error occurs in `BlobController#delete`, it
previously tried to render the `show` view, but that would render a 500
because the view assumes certain instance variables to be present
(e.g. `@last_commit`). Fix this by redirecting back to the blob in
question.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/220168

app/controllers/projects/blob_controller.rb

@@ -94,7 +94,6 @@ class Projects::BlobController < Projects::ApplicationController
   def destroy
     create_commit(Files::DeleteService, success_notice: _("The file has been successfully deleted."),
                                         success_path: -> { after_delete_path },
-                                        failure_view: :show,
                                         failure_path: project_blob_path(@project, @id))
   end
 

changelogs/unreleased/sh-fix-delete-blob-failure.yml

+---
+title: Fix 500 error in BlobController#delete
+merge_request: 34367
+author:
+type: fixed

spec/controllers/projects/blob_controller_spec.rb

@@ -378,6 +378,22 @@ RSpec.describe Projects::BlobController do
 
         expect(response).to redirect_to(after_delete_path)
       end
+
+      context 'when a validation failure occurs' do
+        let(:failure_path) { project_blob_path(project, default_params[:id]) }
+
+        render_views
+
+        it 'redirects to a valid page' do
+          expect_next_instance_of(Files::DeleteService) do |instance|
+            expect(instance).to receive(:validate!).and_raise(Commits::CreateService::ValidationError, "validation error")
+          end
+
+          delete :destroy, params: default_params
+
+          expect(response).to redirect_to(failure_path)
+        end
+      end
     end
 
     context 'if deleted file is the last one in a subdirectory' do